In the manufacture of drawn, extruded and/or ironed containers, one of the problems encountered is to incorporate sufficient rigidity into the bottom wall of the container to prevent buckling when the container is used for packaging pressurized products, such as carbonated beverages.
The most ideal type of container bottom wall would be a flat wall which would allow for maximum capacity for a given container with a minimum height. However, such a container is not economically feasible because the thickness of the wall would have to be of such magnitude that the cost of the container would be prohibitive.
One method that has been employed for maintaining sufficient rigidity with thin metals is to form the bottom wall into a spherical dome configuration. This configuration is generally shown in U.S. Pat. No. 3,760,751. While this configuration allows container manufacturers to somewhat reduce the metal thickness, these manufacturers are continuously working on techniques that will allow for further reduction in metal thickness without sacrificing container rigidity.
Since containers are produced and sold by the billions annually, manufacturers are constantly striving to reduce the wall thickness of the container while still maintaining the same operating characteristics. Because of the large volume, it will be appreciated that a small reduction in metal thickness, even on the order of one thousandth of an inch, will reduce manufacturing costs substantially.
While some small amount of buckling of the bottom wall is tolerable, if the buckle is noticeable, a customer will usually assume that the contents of the can are spoiled which results in substantial waste. It will be appreciated that when packaging pressurized materials, such as beer or other carbonated beverages, the pressure in the container may exceed 50 p.s.i. when the container is stored and subjected to normal summer temperatures and must also be capable of withstanding 90 p.s.i. minimum during the pasteurization process.